G.f. A(x) satisfies A(x) = ( 1 + 9*x*A(x)/(1 - x*A(x)) )^(1/3).

Terms

a(0) =1a(1) =3a(2) =3a(3) =3a(4) =30a(5) =57a(6) =84a(7) =867a(8) =1893a(9) =3162a(10) =33132a(11) =76953a(12) =136812a(13) =1446204a(14) =3478764a(15) =6420387a(16) =68260134a(17) =167946159a(18) =317782524a(19) =3392340186a(20) =8479140510a(21) =16332164868a(22) =174873206424a(23) =442212416121a(24) =863222622780